1. Field of the Invention
The present invention relates to a biosensor and a biosensor system, and further to a method of using the biosensor and biosensor system to detect a target object in a sample.
2. Description of the Related Art
In general, a biosensor is a device that uses a specific biological element or a physical element similar to the biological element to get information from a target object to be measured (i.e., analyte). The detected information is usually transduced by the biosensor into recognizable signals such as colors, fluorescence or electrical signals. With technical advances in modem science, the biosensor is one of the devices that have been developed rapidly.
The application fields of the biosensor are largely divided into six categories. Firstly, biosensors are used mostly in medical field (clinical diagnosis) such as the measurement of blood glucose levels. Besides the measurement of blood glucose levels, the biosensors available in the market or under development analyze and diagnose diverse biomasses including lactic acid, cholesterol, urea and the like. Secondly, biosensors are used for environment applications. In effect, ever increasing needs for environment monitoring will speed up the development of an environment monitoring biosensor. For instance, biosensors are already used to detect biochemical oxygen demand (BOD), cyanide, phenol, heavy metals, pesticides, phosphorus compounds, and nitrogen compounds in sewage. Thirdly, biosensors are used in the field of food safety risk analysis in connection with pesticide residues in food, antibiotics, pathogenic bacteria and other toxic chemical compounds. Fourthly, biosensors are used for military purposes such as in a biochemical weapon sensing biosystem. Since the biochemical weapon sensing must be done very speedily, the biosensor must perform quickly and used frequently. Fifthly, biosensors are used for the analysis of specific chemical substances used in industrial processes including pharmaceutical, chemical, petrochemical processes and so forth. Biosensors are used widely in the fermentation processes of biological industries. Lastly, biosensors are used in laboratories conducting experimental research. In this case, biosensors have special usages and structures. General biosensors are usually built in small sizes allowing for carrying or transport and utilized to analyze specific substances in a real time mode. However, the biosensors for use in experiments are not limited by size, but by analytical capabilities with respect to kinetic analysis on bonding between biomasses, single molecular behavior measurement, and the like.
The biosensor is composed of a bioreceptor which reacts or binds with a specific substance to be detected (i.e., analyte), and a signal transducer which transfers a signal generated by the reaction between the bioreceptor and the analyte. Examples of the bioreceptor include an enzyme, antibody, antigen, membrane, receptor, cell, tissue, and deoxyribonucleic acid (DNA), which selectively reacts and bonds with the analyte. As for the signal transducing method, a variety of physicochemical methods such as electrochemical, fluorescence, color, optical, piezoelectric and SPR (Surface plasmon resonance) are used.
In detail, the optical signal transduction uses a chromogen which changes color at the reaction with oxidase (or bioreceptor). Thus, when a bioreceptor reacts with an analyte, i.e., glucose, the degree of color change in the chromogen is measured. Here, the degree of color change is measured in terms of optical reflectivity or transmittance using a photometer to detect glucose. The electrochemical signal transduction transfers the electrons generated from the oxidation of glucose to an electrode using an electron transfer medium, and measures current flowing through the electrode to detect glucose in blood. According to the signal transduction using fluorescence and color, a label showing fluorescence or color during the reaction between a bioreceptor and an analyte is used. This fluorescence or color development is detected by a laser. Meanwhile, the SPR technology does not use a label material. As its name implies, the SPR uses the surface plasmon resonance phenomenon. More specifically, it monitors, in real-time mode, specific reactions, binding, affinity and kinetic elements between molecules in response to a change in the SPR angle. Lastly, the typical example of the piezoelectric signal transduction is QCM (quartz crystal microbalance). According to the QCM, a metal electrode is attached to both sides of a quartz crystal, and a voltage is impressed thereto. Then, the quartz crystal starts vibrating. This phenomenon is called inverse piezoelectric effect. If a foreign substance is attached to the surfaces of the electrodes, the quartz crystal vibration property is changed. By measuring this change, it becomes possible to observe the movement of the foreign substance on the surfaces of the electrodes.
The above-described signal transducing methods show general similitudes, that is, they detect the reaction or binding between a bioreceptor like enzyme or antibody and an analyte. However, biosensors based on these methods are not economical in that they are applied to specific bioreceptors only, the equipment can be large, or expensive color development reagent or laser are required. Especially, it is difficult to commercialize the methods using a label material because the label material itself and the equipment for detecting the label material are both very expensive.